1. Field of the Invention
This invention relates to an IC device temperature control system which makes it possible to evaluate performance of an IC device correctly and an IC device inspection apparatus incorporating the IC device temperature control system.
2. Description of the Prior Art
Inspection of temperature characteristics of an IC device is carried out in an environment which is held at a predetermined temperature (thermostatic bath or chamber).
The temperature set point of the chamber is set e.g. at -50.degree. C. to +150.degree. C. according to inspection programs.
Further, electric current is supplied to the IC device under test in various patterns according to many different test items of an inspection program. As a result, the IC device generates heat by Joule's law in a different pattern, dependent on the test item. The heat generation is more conspicuous in the case of inspecting an IC device which has a high integration density, such as a microprocessor (MPU) installed in a computer.
In recent years, the processing capacity or speed of microprocessors has been markedly increased, and their integration density has also become higher, resulting in an increased watt density (W/cm.sup.2) of such a microprocessor under test. Therefore, IC devices including MPUs tend to generate a still larger amount of heat.
For example, when a microprocessor generates approximately 30 watts of heat during inspection, the temperature of the microprocessor becomes higher than the set point temperature of the chamber by 40.degree. C. or so.
Further, the amount of heat generated by an IC device becomes larger as the frequency of an electric signal supplied thereto.
Moreover, it is reported that the maximum operating frequency of the microprocessor is lowered with an increase in the temperature of the same due to a lowered switching frequency of transistors, and that if the temperature of the microprocessor rises by 10.degree. C., the maximum operating frequency of the same is reduced by 2%.
For example, when the temperature of a microprocessor capable of operating at a maximum operating frequency of 500 MHz becomes 40.degree. C. higher than the set point temperature of the chamber, the actual maximum operating frequency of the microprocessor falls by no less than 40 MHz. Therefore, the microprocessor which should be ranked in itself in a class in which operation at 500 MHz is ensured is demoted by one grade or class as a microprocessor for operation on the order of 400 MHz.
As a result, yields of microprocessors for operation at high operating frequencies are unduly deteriorated, causing a serious loss.
Further, when there is an increase in heat generation, an IC device is in danger of destroying itself.
Conventionally, with a view to enhancing accuracy of inspection (i.e. yield of properly ranked IC devices) and preventing self-destruction of an IC device, the temperature of the IC device is monitored, and then the IC device is cooled to the set point temperature of the chamber.
The temperature of an IC device can be measured by a method using a contact temperature sensor such as a thermocouple or a non-contact temperature sensor such as an infrared sensor.
Further, another method can be employed in which a temperature sensor is incorporated in an IC device under test and the temperature of the IC device is measured by the temperature sensor, as disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 6-188295.
However, the contact temperature sensor can scratch or soil a package surface of an IC device, causing degradation of the product.
On the other hand, the non-contact temperature sensor such as an infrared sensor cannot measure the temperature of an IC device having a metal surface accurately.
Further, the method using a temperature sensor incorporated in an IC device increases the size and weight of the IC device, resulting in a considerable increase in manufacturing costs of the product.